1. Field of the Invention
The present invention relates to a liquid crystal display device, and more particularly, an in-plane switching mode liquid crystal display device having a high aperture ratio.
2. Discussion of Related Art
Twisted nematic liquid crystal display devices (hereinafter TN LCDs) having high image quality and low power consumption are widely applied to flat panel display devices. The TN LCDs, however, have a narrow viewing angle due to refractive anisotropy of liquid crystal molecules.
To solve this problem, a multi-domain LCD such as a two-domain TN LCD(TDTN LCD) and a domain divided TN LCD(DDTN LCD), and a TN LCD including an optical compensation film have been introduced. In such LCDs, however, a contrast ratio is decreased and a color shift is generated depending on a viewing angle.
Further, for the purpose of a wide viewing angle, an in-plane switching mode LCD is also proposed. The in-plane switching mode liquid crystal display device, which is suggested to materialize wide viewing angle, is disclosed in the JAPAN DISPLAY 92 P547, Japanese Patent Unexamined Publication No. 7-36058, Japanese Patent Unexamined Publication No. 7-225388 and ASIA DISPLAY 95 P707, and etc.
FIG. 1A is a plan view of a unit pixel of a conventional in-plane switching mode active matrix LCD. FIG. 1B is a sectional view according to line I-Ixe2x80x2 of FIG. 1A. As shown in the drawings, the apparatus comprises a gate bus line 1 and a data bus line 2 in which the lines 1, 2 are perpendicularly arranged in a matrix form on a transparent first substrate 10 thereby defining an unit pixel region, a common line 3 arranged parallel to the gate bus line 1 in the pixel region, thin film transistor (TFT) formed adjacent a cross point of the gate bus line 1 and the data bus line 2, and a data electrode 8 and a common electrode 9 formed in the pixel region.
The TFT includes a gate electrode 5 electrically coupled with the gate bus line 1, a gate insulator 12 on the gate electrode 5, a semiconductor layer 15 on the gate insulator 12, a channel layer on the semiconductor layer 15, and source/drain electrodes 6, 7 which are electrically coupled the data bus line 2 and the data electrode 8 respectively.
The common electrode 9 is formed concurrently with the gate electrode 5 and electrically coupled to the common line 3. Further, a passivation layer 20 and a first alignment layer 23a are deposited on the inner surface of the first substrate 10.
On a transparent second substrate 11, a black matrix 28 is formed to prevent a light leakage generating around the TFT, the gate bus line 1, and the data bus line 2. A color filter layer 29, an over-coat layer (not illustrated), and a second alignment layer 23b are formed on the black matrix 28 in sequence. Finally, a liquid crystal layer 30 is formed between the first and second alignment layers 23a, 23b. 
In general, a storage capacitor in a liquid crystal display device is applied to prevent the apparatus from a gray inversion, a flicker, and an afterimage. Methods of forming this storage capacitor are divided into a storage on gate (SOG) mode and a storage on common (SOC) mode. In the SOG mode, some part of the (nxe2x88x921)th gate bus line is applied as a storage capacitor in the nth pixel region. Further, in the SOC mode, a separated electrode for storage capacitor is electrically coupled to the common electrode.
For the use of the above storage capacitor, the aperture ratio is decreased, and the metal lines may cause a short state, thereby decreasing a yield.
Accordingly, the present invention is directed to an in-plane switching mode LCD that substantially obviates one or more of the problems due to limitations and disadvantages of the related art.
An object of the present invention is to provide an in-plane switching mode LCD having the high aperture ratio and the high yield by using the SOG mode storage capacitor only, or both SOG mode storage capacitor and SOC mode storage capacitor.
Additional features and advantages of the invention will be set forth in the description which follows and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
In order to achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, an in-plane switching mode liquid crystal display device comprises first and second substrates; a data bus line and a gate bus line arranged in a matrix on said first substrate and defining a unit pixel region; a thin film transistor (TFT) formed adjacent a cross point of the gate bus line and the data bus line, and a data electrode which partially covers adjacent the gate bus line; a passivation layer on the TFT and the data electrode; a common electrode substantially parallel to the data electrode and covering the gate bus lines of nth and (n+1)th, or nth and (nxe2x88x921)th; a common line covering the gate bus lines of nth and (n+1)th, or nth and (nxe2x88x921)th; a first alignment layer on the common electrode; a black matrix for preventing a light leakage which is generated around the TFT, the gate bus line, and the data bus line; a color filter layer and a second alignment layer on the black matrix in sequence; and a liquid crystal layer between said first and second substrates.
A storage capacitor is formed by the gate bus line, the data electrode, and the common electrode or the common line.
In another embodiment according to the present invention, certain part of the data electrode covers the nth gate bus line. In addition, a part of the common electrode covers adjacent the data electrode and another part of the common electrode does not cover the opposite data electrode and the gate bus line. In this case, the storage capacitor is formed by the gate bus line, the data electrode, and the common electrode or the common line.
According to another embodiment of the present invention, a liquid crystal display device has a substrate, first and second gate lines arranged substantially in parallel above the substrate, a bus line arranged to intersect the first and second gate lines to define a pixel, a transistor having a source and a drain formed near an intersection part of the bus line and the first gate line, the source being connected to the bus line, and at least one data electrode connected to the drain of the transistor. A passivation layer is generally formed above the transistors and the at least one data electrode. Moreover, at least one common electrode is arranged above the passivation layer in parallel with the second gate line, the common electrode and the data electrode. In this configuration, the portions of at least two of the second gate line, the data electrode and the common electrode are overlapping with each other.
According to one feature of the present invention, the portions of the second gate line, the data electrode and the common electrode all overlap with each other. Alternatively, the second gate line has no overlapping portions with the data electrode and the common electrode.
According to another feature of the present invention, the data electrode has no overlapping portions with the common electrode. Alternatively, the second gate line has no overlapping portions with the common electrode.